This invention is directed to film compositions, structure applications, and methods for making nanostructured and nanoporous films of metals or metal oxides. These films are derived from precursor formulations containing metal-organic compounds. Throughout this document xe2x80x9cnanostructured filmsxe2x80x9d refers to thin films with nanoparticles in the structure or nanoscale domain structure, and xe2x80x9cnanoporous filmsxe2x80x9d refers to thin films with pores with diameters in the nanometer range. The invention also relates to the use of such films in a variety of applications, including but not limited to those that apply to the microelectronics industry.
Semiconductors are widely used as the basis for forming integrated circuits for use in electronic devices such as computers, televisions, PDAs, radios, cell phones, etc. These integrated circuits typically combine millions of transistors on a single crystal silicon chip to perform complex functions and to store data. Due to the continuing trend of miniturization as well as other industry demands, semiconductor microelectronic designers require integrated circuits that are (1) higher in speed, (2) well-controlled for film nanoconstituents or nanoparticles and the resulting nanostructure, and (3) lower in cost.
1. Achieving Higher Speed in Microelectronic Circuits
One way to make the integrated circuits faster is to reduce signal cross talk. Cross talk signals are signals on a first conductor wire that couple to a second conductor wire in close proximity to the first conductor wire and create incorrect signals on the second conductor wire. Decreasing the capacitance between the conductor wires will reduce cross talk signals. The capacitance between the conductor wires can be decreased by decreasing the insulator dielectric constant of the materials between the conductor wires. Many insulator dielectric constant reduction schemes are being studied, such as using acrogel films (which are nanoporous dielectric films where the solid dielectric material has many voids that are filled with air). In U.S. Pat. No. 6,380,105, xe2x80x9cLow volatility solvent-based method for forming thin film nanoporous aerogels on semiconductor substrates,xe2x80x9d a fabrication method for thin film nanoporous dielectric materials is disclosed. However, these films are formed using normal VLSI (Very Large Scale Integration) techniques, which makes the films difficult to pattern and produces variable results in terms of controlling their porosity because (1) the photoresists normally applied to image a VLSI film fill the voids with an unwanted residual and (2) the solvent chemistry that is used to remove the photoresist fills the voids with unwanted residual solvents. It is difficult to remove these unwanted residual photoresist materials and residual solvent chemistry. Thus there exists a need to control the porosity of a nanoporous film as well as to be able to easily pattern these films without creating difficult to remove residuals.
(2) Controlling Film Nanoconstituents or Nanoparticles and Resulting Nanostructure in Microelectronic Circuits
Another need in VLSI processing and design is the need to control the nanostructure of a film. Indeed, advanced design thin films for use in VLSI, such as metal or insulative diffusion barriers, conductive electrodes for capacitors, wiring conductors, thin film resistors, thin film fuses, thin film magnetic films and thin film dielectric materials, attempt to control the nanoconstituents or nanoparticles. By controlling the nanoparticles in these thin films one may control the final nanostructure of the film.
(3) Achieving Lower Costs in Microelectronic Circuits
Another need in VLSI design and manufacture is to simplify the process of producing circuits on semiconductor substrates. It is also beneficial to simplify the process without increasing the cost of manufacture, preferably lowering the manufacturing cost. In the traditional VLSI approach, a necessary series of process steps involves the photolithography process that defines patterns in films. This is also a large cost in the traditional VLSI approach. Basically, for every film patterned in VLSI, a photoresist needs to be exposed and imaged, developed and used as a mask to transfer the image through a Reactive Ion Etch (RIE) and then the unwanted photoresist is removed using a plasma O2 ash or a wet solvent strip followed by a cleaning step to remove photoresist residuals. Indeed, one can see that defining a pattern on any film layer used in VLSI is costly just from the sheer number of steps. In U.S. Pat. No. 5,534,312, xe2x80x9cMethod for directly depositing metal containing patterned films,xe2x80x9d a photoresist-free method for making patterned films of metal oxides, metals, or other metal containing compounds is described. Specifically this process is a method of photochemical metal organic deposition (PMOD).
The method involves applying an amorphous film of a metal-organic compound to a substrate. The film may be conveniently applied by spin coating using standard industry techniques. The metal-organic compound used is photoreactive and undergoes a low temperature chemical reaction initiated by light of a suitable wavelength. The end product of the reaction depends upon the atmosphere in which the reaction is carried out. For example, metal oxide films may be made in air. Films may be patterned by exposing only selected portions of the film to light. Patterns of two or more materials may be laid down from the same film by exposing different parts of the film to light in different atmospheres. The resulting patterned film is generally planar, eliminating the need for separate planarization steps. It has been found that this PMOD technique can be applied to create controlled nanoporous or nanostructured films. As can be seen, this process indeed simplifies the overall process and creates a lower cost VLSI processing method. As noted above, nanoporosity is a desirable characteristic in certain films for improving qualities such as dielectric constant. However, because the ""312 patent does not address nanoporous films nor the control of nanoporosity in such films, there still exists a need to combine the simplified, low-cost PMOD method of creating patterned films used in VLSI with a way to effectively control nanoporosity in a film.
The present invention discloses a method for the controlled deposition of nanoporous or nanostructured thin films. The process consists of first depositing a precursor film on a substrate. The precursor formulation may be deposited on the surface by a variety of methods, such as spin coating. The deposition may be carried out at room temperature. The next step is converting the precursor solution into a metal or metal oxide film.
To create a nanostructured film according to the present invention, a least one of the components of the precursor formulation is partially or fully converted to a metal or metal oxide. This is followed by the conversion of the second component. At least one of these two conversion steps may be accomplished by photolysis (decomposition of precursor film via photochemical reaction of the precursor compound) or by the impact of an ion or an electron beam. The resulting film created is a well-controlled, nanostructured thin film where each component can be independently controlled. During the conversion step, a light, ion, or electron beam is imaged through a mask. The resulting thin film has regions where the conversion step caused a reaction and in other regions there will be no reaction. Therefore, by use of a mask or directed beam, the nanostructured metal or metal oxide film is patterned.
By altering the atmosphere in which the pattern is formed, the composition and resulting nanostructure and hence the thin film properties of the resulting metal or metal oxide film can be altered. The process also includes the atmospheric reaction being performed (1) before, (2) during, or (3) after, the light, ion, or electron beam conversion step or (4), any combination of (1), (2) or (3).
By making a nanostructured film where one component is easily removed, a nanoporous film may be prepared. Additionally, process related variables such as those described herein may be used to influence the porosity of the photolyzed film.